<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    ul {
      margin: 100px auto;
      display: flex;
      /* flex-wrap: wrap;
      flex-direction: row;
       */
      flex-flow: row wrap;
      list-style: none;                         
      width: 600px;
      justify-content: space-around;
      align-items: center;
      align-content: space-around;
      /* align-items: stretch; */
      height: 700px;
      background-color: skyblue;
    }

    li {
      /* float: left; */
      height: 100px;
      width: 90px;
      background-color: antiquewhite;
    }

    .item1 {
      height: 200px;
    }

    .item2 {
      font-size: 40px;
      height: 200px;
    }

    .item3 {
      height: 300px;
    }
  </style>
</head>

<body>
  <ul>
    <li class="item1">1</li>
    <li class="item2">2</li>
    <li class="item3">3</li>
    <li class="item">4</li>
    <li class="item">5</li>
    <li class="item">6</li>
    <li class="item">7</li>
    <li class="item">8</li>
    <li class="item">9</li>
    <li class="item">10</li>
    <li class="item">11</li>
    <li class="item">12</li>
    <li class="item">13</li>
    <li class="item">14</li>
    <li class="item">15</li>
    <li class="item">16</li>
  </ul>
</body>

</html>